Method and system for recovering fluid

ABSTRACT

Methods and systems for recovering retained filtered fluid are provided.

BACKGROUND OF THE INVENTION

After using a filter device to filter fluid in a closed system, aresidual volume of filtered fluid can be retained between the downstreamside of the filter medium and the filtered fluid receiving container forthe filtered fluid. Some filtered fluids, e.g., those used in thepharmaceutical industry, are expensive, and thus, the loss of this fluidvolume (for example, during the manufacture of biological therapeutics)can be costly. Further, during clinical trials, non-recoverable productmay prevent manufacturers from preparing an adequate quantity ofproduct, adversely impacting the ability to generate critical data thatcould lead to beneficial treatment. Cumulatively, the loss of even a fewmilliliters of fluid per filtration, can represent a significant amountof money.

There is a need for improved methods and systems for recovering retainedfiltered fluid.

The present invention provides for ameliorating at least some of thedisadvantages of the prior art. These and other advantages of thepresent invention will be apparent from the description as set forthbelow.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the invention provides a method for recovering filteredfluid retained in a filter system including a filter device comprising ahousing having an inlet and an outlet defining a filtration flow pathbetween the inlet and the outlet, and a porous filter medium across thefiltration flow path, the porous medium having an upstream side and adownstream side; the system also including a filtered fluid receivingcontainer arranged downstream of the outlet; a first fluid flow pathbetween the outlet and the filtered fluid receiving container; a secondfluid flow path between the first fluid flow path and the filtered fluidreceiving container; wherein the second fluid flow path is connected tothe first fluid flow path; the method comprising: (a) passing sterileair and/or sterile gas through the outlet of the filter device and alongthe first fluid flow path into the filtered fluid receiving container;(b) passing fluid to be filtered along the filtration flow path throughthe filter device and passing filtered fluid along the first fluid flowpath into the filtered fluid receiving container, wherein a volume offiltered fluid is retained in the housing between the downstream side ofthe porous filter medium and the outlet; and, (c) allowing the sterileair and/or sterile gas to pass from the filtered fluid receivingcontainer along the second fluid flow path into the first fluid flowpath and through the outlet into the housing of the filter device, anddisplacing retained filtered fluid along the first fluid flow path intothe filtered fluid receiving container.

Another embodiment of the invention provides a method for recoveringfiltered fluid retained in a filter system including a filter devicecomprising a housing having an inlet and an outlet defining a filtrationflow path between the inlet and the outlet, and a porous filter mediumacross the filtration flow path, the porous medium having an upstreamside and a downstream side; the system also including a filtered fluidreceiving container arranged downstream of the outlet; a first fluidflow path between the outlet and the filtered fluid receiving container;a second fluid flow path between the first fluid flow path and thefiltered fluid receiving container; wherein the second fluid flow pathis connected to the first fluid flow path; the method comprising: (a)filtering fluid by passing the fluid along the filtration flow paththrough the filter device and along the first fluid flow path into thefiltered fluid receiving container, including displacing, by thefiltered fluid, sterile air and/or sterile gas into the filtered fluidreceiving container, wherein a volume of filtered fluid is retained inthe housing between the downstream side of the porous filter medium andthe outlet; and, (b) allowing the sterile air and/or the sterile gas topass from the filtered fluid receiving container along the second fluidflow path into the first fluid flow path and through the outlet into thehousing of the filter device, and displacing retained filtered fluidinto the filtered fluid receiving container.

In another embodiment, a system for recovering filtered fluid comprises(a) a filter device comprising a housing having an inlet and an outletdefining a filtration flow path between the inlet and the outlet, and aporous filter medium across the filtration flow path, the porous mediumhaving an upstream side and a downstream side; (b) a filtered fluidreceiving container arranged downstream of the outlet; (c) a first fluidflow path between the outlet and the filtered fluid receiving container;and (d) a second fluid flow path between the first fluid flow path andthe filtered fluid receiving container; wherein the second fluid flowpath is connected to the first fluid flow path.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is an illustrative schematic of two systems according toembodiments of the invention, wherein one system includes a sterilizinggas filter upstream of a second filter, and the other system includesthe second filter, without the sterilizing gas filter.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention provides a method for recovering filteredfluid retained in a filter system including a filter device comprising ahousing having an inlet and an outlet defining a filtration flow pathbetween the inlet and the outlet, and a porous filter medium across thefiltration flow path, the porous medium having an upstream side and adownstream side; the system also including a filtered fluid receivingcontainer arranged downstream of the outlet; a first fluid flow pathbetween the outlet and the filtered fluid receiving container; a secondfluid flow path between the first fluid flow path and the filtered fluidreceiving container; wherein the second fluid flow path is connected tothe first fluid flow path; the method comprising: (a) passing sterileair and/or sterile gas through the outlet of the filter device and alongthe first fluid flow path into the filtered fluid receiving container;(b) passing fluid to be filtered along the filtration flow path throughthe filter device and passing filtered fluid along the first fluid flowpath into the filtered fluid receiving container, wherein a volume offiltered fluid is retained in the housing between the downstream side ofthe porous filter medium and the outlet; and, (c) allowing the sterileair and/or sterile gas to pass from the filtered fluid receivingcontainer along the second fluid flow path into the first fluid flowpath and through the outlet into the housing of the filter device, anddisplacing retained filtered fluid along the first fluid flow path intothe filtered fluid receiving container.

Embodiments of the method can include passing air and/or gas through asterilizing grade porous filter medium to produce the sterile air and/orthe sterile gas, before passing the sterile air and/or the sterile gasalong the filtration fluid flow path.

For example, in one embodiment of the method, the filter devicecomprises a sterilizing grade filter and passing air and/or gas throughthe sterilizing grade filter device along the filtration flow pathprovides the sterile air and/or sterile gas passing through the outletof the filter device. Alternatively, or additionally, an embodiment ofthe method comprises passing air and/or gas through an additional filterdevice which is an upstream sterilizing grade filter device to providesterile air and/or sterile gas, and subsequently passing the sterile airand/or sterile gas through the filter device used to filter fluid.

If desired, the method can also include, while filtering fluid bypassing the fluid along the filtration flow path through the filterdevice and along the fluid flow path into the filtered fluid receivingcontainer, displacing, by the filtered fluid, sterile air and/or sterilegas into the filtered fluid receiving container, wherein a volume offiltered fluid is retained in the housing between the downstream side ofthe porous filter medium and the outlet; and, allowing the sterile airand/or the sterile gas to pass from the filtered fluid receivingcontainer along the fluid flow path and through the outlet into thehousing of the filter device, and displacing retained filtered fluidinto the filtered fluid receiving container.

Another embodiment of the invention provides a method for recoveringfiltered fluid retained in a filter system including a filter devicecomprising a housing having an inlet and an outlet defining a filtrationflow path between the inlet and the outlet, and a porous filter mediumacross the filtration flow path, the porous medium having an upstreamside and a downstream side; the system also including a filtered fluidreceiving container arranged downstream of the outlet; a first fluidflow path between the outlet and the filtered fluid receiving container;a second fluid flow path between the first fluid flow path and thefiltered fluid receiving container; wherein the second fluid flow pathis connected to the first fluid flow path; the method comprising: (a)filtering fluid by passing the fluid along the filtration flow paththrough the filter device and along the first fluid flow path into thefiltered fluid receiving container, including displacing, by thefiltered fluid, sterile air and/or sterile gas into the filtered fluidreceiving container, wherein a volume of filtered fluid is retained inthe housing between the downstream side of the porous filter medium andthe outlet; and, (b) allowing the sterile air and/or the sterile gas topass from the filtered fluid receiving container along the second fluidflow path into the first fluid flow path and through the outlet into thehousing of the filter device, and displacing retained filtered fluidinto the filtered fluid receiving container.

In another embodiment, a system for recovering filtered fluid comprises(a) a filter device comprising a housing having an inlet and an outletdefining a filtration flow path between the inlet and the outlet, and aporous filter medium across the filtration flow path, the porous mediumhaving an upstream side and a downstream side; (b) a filtered fluidreceiving container arranged downstream of the outlet; (c) a first fluidflow path between the outlet and the filtered fluid receiving container;and (d) a second fluid flow path between the first fluid flow path andthe filtered fluid receiving container; wherein the second fluid flowpath is connected to the first fluid flow path.

Embodiments of the method can include introducing gas and/or air intothe filter system before filter integrity testing or during filterintegrity testing using forward flow or bubble point test methods, or aspart of any system leak test procedures.

For example, in one embodiment of the method, the filter devicecomprises a sterilizing grade filter and passing air and/or gas throughthe sterilizing grade filter device provides the sterile air and/orsterile gas passing through the outlet of the filter device.Alternatively, or additionally, an embodiment of the method comprisespassing air and/or gas through an additional filter device which is anupstream sterilizing grade filter device to provide sterile air and/orsterile gas, and subsequently passing the sterile air and/or sterile gasthrough the filter device used to filter fluid.

Typically, an embodiment of the method further comprises passing thefiltered fluid from the filtered fluid receiving container for furtherprocessing, which may include, for example, other intermediate stages ofany process that requires the continued use of a closed system, alsoincluding filling receptacles such as syringes, vials, ampoules,bottles, bioprocessing containers, bottles, and/or carbouys.

Advantageously, embodiments of the invention are compatible withprocesses involving integrity testing of filter devices and filtersystems.

Embodiments of the invention are suitable for use in a variety ofsystems, including closed systems, particularly bioprocessing systems.

Embodiments of the invention are suitable for use with a variety offluids to be filtered, for example, cell culture (e.g., including batchand fed-batch operations of suspension and adherent cell lines),preparing sterile or low bioburden fluids for the pharmaceutical and/orbiopharmaceutical industries, including drugs, vaccines, and intravenousfluids, antibody- and/or protein-containing fluids, and/or fluids forthe food and beverage industry.

A variety of filter devices, and containers, typically flexible (e.g.,plastic) containers and conduits, including commercially availablefilter devices, containers, and conduits, are suitable for use inembodiments of the invention, and are known in the art. Suitableconnectors, e.g., conduit connectors; moulded tubing; and flow controldevices such as clamps, seals, valves, transfer leg closures, and thelike, are known in the art.

In the following discussion, it should be recognized that sterile gasand sterile air can be used equivalently, e.g., embodiments referred tosterile gas also encompass the use of sterile air, and vice versa.

As used herein, the term “closed” refers to a system that allows thecollection and processing (including filtration, and, if desired, themanipulation, e.g., separation of portions, separation into components,storage, and preservation) of fluid, without exposing the contents ofthe system to the environment in which it is being used. A closed systemcan be as originally made, or result from the connection of systemcomponents of sanitary fittings including sterile docking devices.

Each of the components of the invention will now be described in moredetail below, wherein like components have like reference numbers.

FIG. 1 illustrates two embodiments of filter systems according to theinvention. One embodiment of the system, 1000, is shown within dottedlines. Another embodiment of the system, 2000, includes the embodimentof the system 1000, and includes additional components, includingupstream sterilizing grade filter device 700. The embodiments of thesystems are discussed in more detail below.

The illustrated embodiment of the system 1000 includes a filter device500 comprising a housing 510 having an inlet 511 and an outlet 512defining a filtration flow path 550 between the inlet and the outlet,and a porous filtration medium 501 having an upstream side 501A and adownstream side 501B across the filtration flow path. The filter devicetypically has at least a bacterial removal rated porous filtrationmedium, and can have a sterilizing grade porous filtration medium. Thefiltration medium can have a variety of configurations, includingplanar, pleated and/or hollow cylindrical. Typically, the filter deviceis vented during the initial filtration of liquid so that the maximumavailable filter medium surface is used, and to prevent build-up of airor gas in the system. After the filter device housing is filled withliquid, the vent can be closed. Preferably, the filter device includes avent, or vents can be arranged upstream and/or downstream of the filterdevice, so that air or gas can be vented from the system beforefiltration of the liquid is carried out.

One end of a conduit 10 is placed in fluid communication with the filterdevice inlet.

A filtered fluid receiving container 50 is arranged downstream of theoutlet 512, and a first fluid flow path 200 shown comprising conduits201A, 201B, 201C (shown connected by connectors 240 and 250(alternatively, conduits can be moulded together); in some embodimentsthe first fluid flow path comprises a single conduit, or more than threeconduits) is provided between the outlet 512 and the filtered fluidreceiving container 50. Connector 250 is optional, and included ifconduit 300 is present.

The illustrated embodiment of the filter system also includes an airand/or gas processing system 600 including a second fluid flow path 601comprising at least one conduit, wherein the second fluid flow path isin fluid communication with the filtered fluid receiving container 50 atone end of the flow path and in fluid communication with the first fluidflow path 200 at the other end (shown in fluid connection via connector240, alternatively, conduits can be moulded together). The illustratedsecond fluid flow path 601 includes an optional flow control device 675(e.g., a valve or clamp) arranged between the ends of the flow path(e.g., the flow control device can be external to the conduit (e.g., aclamp that can compress the conduit) or within or between theconduit(s)).

Optionally, the system can include additional components, for example,FIG. 1 shows a flow control device 402.

Some embodiments of the method and system do not require the presence oruse of flow control devices. However, in some other embodiments, flowcontrol devices are associated with various conduits to allow or preventflow through the conduits. Initially, the various flow control devicesare closed to prevent flow through the conduits.

In one embodiment of the method, a container A containing the fluid tobe filtered is connected to conduit 10. The system 1000 is arrangedvertically, wherein the end of second flow path 601 where it connectswith container 50 is at the highest point of the container. Preferably,the filtered fluid receiving container 50 is arranged such that thefirst fluid flow path is free-draining between the outlet of the filterand the receiving fluid container.

Fluid is filtered as it passes along the filtration flow path 550through the porous medium 501. The filtered fluid (liquid) displacessterile air ahead of it, and the displaced air, and filtered fluid, passalong the first fluid flow path 200 into the filtered fluid receivingcontainer 50.

After filtration is completed, filtered fluid is retained in the filterdevice housing 510 between the downstream side 501B of the porousfiltration medium and the housing outlet 512, and possibly in the fluidflow path 200.

After filtration, flow control device 675 is opened, and sterile airpasses from the filtered fluid receiving container 50 (along with someair in 601 as far as flow control device 675) along the second fluidflow path 601 and through connector 240 into the upper part of the firstflow path 200 via conduit 201A and through the outlet 512 of the filterdevice 500, and retained filtered fluid passes from the filter devicehousing and device outlet along the first fluid flow path into thefiltered fluid receiving container 50.

As noted above, in accordance with any embodiment of the invention, thepresence of flow control device 675 is optional, alternatively, ifpresent, the flow control device 675 can be kept open while carrying outembodiments of the method. For example, once sufficient air or gas ispresent in receiving container 50 and in the second flow path relativeto the downstream hold up volume in the filter device and conduits, thenonce filtration starts, the system will “self-recover” and sterile airor gas passes from the filtered fluid receiving container 50 along thesecond fluid flow path 601 and through connector 240 into the upper partof the first flow path 200 via conduit 201A and through the outlet 512of the filter device 500, and retained filtered fluid passes from thefilter device housing and device outlet along the first fluid flow pathinto the filtered fluid receiving container 50.

If desired, the filtered fluid receiving container can be asepticallydisconnected from the system to maintain closure and moved to anotherlocation where the collected filtered fluid can be removed from thecontainer.

Some embodiments of the method and system do not require the presence oruse of an upstream sterilizing grade filter device. For example, asdiscussed above, the filter device 500 can comprise a sterilizing gradefilter and passing air and/or gas through the sterilizing grade filterdevice along the filtration flow path provides the sterile air and/orsterile gas passing through the outlet of the filter device.Alternatively, or additionally, the end-user may be satisfied that theassembled system has been manufactured with a satisfactory low bioburdenand/or have a clean enough air supply for the end-user's qualitystandards such that an upstream sterilizing grade filter device is notrequired. Alternatively, or additionally, the assembler of the systemhas filled the components of the system that need to receive air or gaswith air or gas at the end of system assembly, but before the system isirradiated/subject to the preferred method of sterilization and shipped.

As noted above, the embodiment of the system 2000, includes theembodiment of the system 1000, and includes additional optionalcomponents, including an optional upstream sterilizing grade filterdevice 700, as well as pumps 801 and 802, connector 250, conduits 300and 301, e.g., for connection to the next stage in processing, as wellas flow control devices (such as clamps or valves) 401, and 403, andconnectors 701 and 702.

In one embodiment, wherein the system includes conduit 301 and flowcontrol device 403, flow control device 403 is initially closed (if flowcontrol device 402 is present, it is initially open), after filtration,and after retained filtered fluid is passed into the filtered fluidreceiving container, as described above, flow control device 403 isopened and pump 802 is operated such that fluid is passed along conduit301 to the next stage of processing.

In another embodiment of the method, sterile air and/or sterile gas isintroduced into the system 1000 before filtering the fluid.Illustratively, with respect to the embodiment of the system 2000, anoptional sterilizing grade filtration device 700 is placed in fluidcommunication with conduit 10, flow control device 403 is closed, andgas or air is passed through the sterile filtration device (e.g., usinga compressor, either directly from the compressor or via an instrumentsuch as a filter integrity tester or a system leak tester) to providesterile gas and/or sterile air which subsequently passes through thefiltration device 500, along the filtration flow path 550 through theporous filtration medium 501 and along the fluid flow path 200 into thefiltered fluid receiving container 50

A source container A containing the fluid to be filtered is placed incommunication with conduit 10. Typically, the system includes aconnector such that this container A, and the sterilizing grade filterdevice 700 can both be placed in communication with the conduit 10.Before liquid is filtered, flow control device 401 is closed.

Fluid is filtered as it passes along the filtration flow path 550through the porous medium 501. Since sterile air is present in thesystem, the filtered fluid (liquid) displaces sterile air ahead of it,and the displaced air, and filtered fluid, pass along the first fluidflow path 200 into the filtered fluid receiving container 50.

After filtration is completed, filtered fluid is retained in the filterdevice housing 510 between the downstream side 501B of the porousfiltration medium and the housing outlet 512, and possibly in the fluidflow path 200.

After filtration, flow control device 675 is opened, and sterile airpasses from the filtered fluid receiving container 50 (along with someair in 601 as far as flow control device 675) along the second fluidflow path 601 and through connector 240 into the upper part of the firstflow path 200 via conduit 201A and through the outlet 512 of the filterdevice 500, and retained filtered fluid passes from the filter devicehousing and device outlet along the first fluid flow path into thefiltered fluid receiving container 50. If desired, flow control device403 is opened, and pump 802 is operated such that fluid is passed alongconduit 301 to the next stage of processing.

In another embodiment, gas or air can be introduced and passed into thefiltered fluid receiving container 50 while flow control devices 401 and402 are open, and flow control devices 404 and 675 (and 403, if present)are closed. After the gas or air is introduced flow control device 401is closed and flow control device 404 is opened. A small amount ofliquid (water or pharmaceutical fluid) can be passed through the filterdevice 500 to flush the filter device before use, and the fluid can beflushed through connector 250 and conduit 300. Subsequently, flowcontrol device 402 is closed, and filtration proceeds, including passingfiltered fluid along conduit 300 (rather than into container 50), andopening flow control device 675 to recover retained filtered fluid asdiscussed above, and the recovered fluid is passed along conduit 300 forfurther processing.

In yet another embodiment, gas or air can be introduced and passed intothe filtered fluid receiving container 50 while flow control devices 401and 402 are open and flow control devices 675, 403 and 404 are closed.Flow control device 404 is opened, and a small amount of liquid (wateror pharmaceutical fluid) can be passed through the filter device 500 toflush the filter device at least once before use, and passed throughconnector 250 and conduit 300. Subsequently, flow control device 402 isopened and flow control device 404 is closed, and filtration proceedswith filtered fluid passing into receiving container 50. Afterfiltration is completed, flow control device 675 is opened, allowing gasor air to pass along fluid flow path 200 and retained fluid to berecovered into container 50. If desired, flow control device 403 isopened, and pump 802 is operated such that fluid is passed along conduit301 to the next stage of processing.

If desired, in accordance with any embodiment of the method, thefiltered fluid can be passed from the filtered fluid receiving containerelsewhere for further processing.

The following example further illustrates the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLE

This example demonstrates that filtered fluid remaining in the systemafter filtration can be recovered in accordance with an embodiment ofthe invention.

A system 2000 is set up as generally shown in FIG. 1.

The system includes a sterilizing grade filter devices 700 and 500 (500is a KLEENPAK™ Capsule Filter (Pall Corporation, Port Washington,N.Y.)), flexible tubing, and a flexible bag (the filtered fluidreceiving container 50).

Flow control device 401 is opened, and gas is passed through thesterilizing grade filter device 700 via a compressor, and the sterilegas is passed through filter device 500 into the filtered fluidreceiving container 50. Flow control device 401 is closed.

A flexible bag containing 10 L of fluid to be filtered is attached tothe system, and the system is arranged in a free draining orientation,and fluid is introduced initially using a pump and the filtration deviceis vented, and then filtration is performed using a peristaltic pump ata rate of up to 2 L/min.

Air is displaced by the fluid passing through the system, and thedisplaced air and filtered fluid passes into the filtered fluidreceiving container.

After filtration is completed, flow control device 675 (a clamp on theconduit 601) is opened, allowing air to pass upwardly and throughconduit 201A and the outlet 512 of the filter device. The air enteringthe filter device housing 510 displaces filtered fluid retained in thefilter device (downstream of the filter medium 501) and filtered fluidretained in the tubing 201A, 201B downstream of the filter device, andthe displaced filtered fluid is collected in the filtered fluidreceiving container. An additional volume of about 50 mL of filteredfluid is recovered.

Subsequently, the filtered fluid is passed along conduit 301 for furtherprocessing.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. A method for recovering filtered fluid retained in a filter systemincluding a filter device comprising a housing having an inlet and anoutlet defining a filtration flow path between the inlet and the outlet,and a porous filter medium across the filtration flow path, the porousmedium having an upstream side and a downstream side; the system alsoincluding a filtered fluid receiving container arranged downstream ofthe outlet; a first fluid flow path between the outlet and the filteredfluid receiving container; a second fluid flow path between the firstfluid flow path and the filtered fluid receiving container; wherein thesecond fluid flow path is connected to the first fluid flow path; themethod comprising: (a) passing sterile air and/or sterile gas throughthe outlet of the filter device and along the first fluid flow path intothe filtered fluid receiving container; (b) passing fluid to be filteredalong the filtration flow path through the filter device and passingfiltered fluid along the first fluid flow path into the filtered fluidreceiving container, wherein a volume of filtered fluid is retained inthe housing between the downstream side of the porous filter medium andthe outlet; and, (c) allowing the sterile air and/or sterile gas to passfrom the filtered fluid receiving container along the second fluid flowpath into the first fluid flow path and through the outlet into thehousing of the filter device, and displacing retained filtered fluidalong the first fluid flow path into the filtered fluid receivingcontainer.
 2. A method for recovering filtered fluid retained in afilter system including a filter device comprising a housing having aninlet and an outlet defining a filtration flow path between the inletand the outlet, and a porous filter medium across the filtration flowpath, the porous medium having an upstream side and a downstream side;the system also including a filtered fluid receiving container arrangeddownstream of the outlet; a first fluid flow path between the outlet andthe filtered fluid receiving container; a second fluid flow path betweenthe first fluid flow path and the filtered fluid receiving container;wherein the second fluid flow path is connected to the first fluid flowpath; the method comprising: (a) filtering fluid by passing the fluidalong the filtration flow path through the filter device and along thefirst fluid flow path into the filtered fluid receiving container,including displacing, by the filtered fluid, sterile air and/or sterilegas into the filtered fluid receiving container, wherein a volume offiltered fluid is retained in the housing between the downstream side ofthe porous filter medium and the outlet; and, (b) allowing the sterileair and/or the sterile gas to pass from the filtered fluid receivingcontainer along the second fluid flow path into the first fluid flowpath and through the outlet into the housing of the filter device, anddisplacing retained filtered fluid into the filtered fluid receivingcontainer.
 3. The method of claim 1, including passing air and/or gasthrough a sterilizing grade porous filter medium to produce the sterileair and/or the sterile gas, before passing the sterile air and/or thesterile gas along the filtration fluid flow path.
 4. A filter systemcomprising: (a) a filter device comprising a housing having an inlet andan outlet defining a filtration flow path between the inlet and theoutlet, and a porous filter medium across the filtration flow path, theporous medium having an upstream side and a downstream side; (b) afiltered fluid receiving container arranged downstream of the outlet;(c) a first fluid flow path between the outlet and the filtered fluidreceiving container; and, (d) a second fluid flow path between the firstfluid flow path and the filtered fluid receiving container; wherein thesecond fluid flow path is connected to the first fluid flow path.
 5. Thesystem of claim 4, further comprising a sterilizing grade filter devicearranged upstream of the filter device in (a).